The present relates generally to fabrication of object and prototypes through the sequential deposition of material. More particularly, the invention relates to object fabrication using ultrasonic, electrical resistance, and frictional consolidation methodologies.
Numerous manufacturing technologies exist for producing objects sequentially adding material, with the casting of liquid metal being perhaps the oldest such technique. In the past two decades, however various processes for fabricating objects to net shape primarily through material addition, i.e. without a finishing step such as machining to produce detailed, high-precision features, have been patented and, in a few cases, commercialized.
Most of these additive manufacturing processes either rely on an adhesive, or a solidification process in order to produce a bond between previously deposited material and each incremental volume of material which is added. Although the use of adhesives is convenient, the properties of the adhesive control the properties of the finished object, and the limits the usefulness of such processes in the production of engineering parts and products.
Particularly with regard to the production of metal objects, prior-art methods based on solidification transformation require to presence of liquid metal. Various approaches to the problem include three-dimensional shape melting or shape welding as described by Edmonds, U.S. Pat. No. 4,775,092, Doyle et al., U.S. Pat. No. 4,812,186, and Prinz et al., U.S. Pat. No. 5,207,371, and laser melting and deposition of powders as described in Lewis et. al, U.S. Pat. No. 5,837,960. Brazing of laminated objects, and closely related to it, infiltration of a low-surface tension and low-melting point alloy to fill voids in objects made by compacting or printing metal powders have also been employed, see U.S. Pat. No. 5,807,437 to Sachs; U.S. Pat. No. 5,872,714 to Shaikh; and U.S. Pat. No. 5,354,414 to Feygin. All of these processes require high temperatures and formation of liquid metals to produce a metal part
The presence of liquid metal in a process presents numerous safety and material handling problems. In addition, the presence of liquid metal in additive manufacturing processes may detrimentally effect dimensional accuracy of a part when built. The dimensional changes which occur during the liquid-solid transformation in metals are not wholly consistent, and are subject to random noise, see xe2x80x9cEffects of Random Noise Shrinkage on Rapid Tooling Accuracy,xe2x80x9d by Paul Jacobs, Materials and Design, Vol. 21, No. 2, April 2000, pp. 127-136. This noise results in unpredictable and uncontrollable dimensional inaccuracies. As part size increases, the errors accumulate, making it impossible to produce accurate parts. Several solutions have been proposed, including the use of a second, subtractive step for addressing the accuracy issues. However, this adds time, cost, and complexity to the process.
The only commercialized low-temperature process for additive manufacturing of engineering scale metal components is electroforming, or plating. In the electroforming process, metal salts are dissolved in an aqueous solution. When an electrical current passes through this bath, metal is deposited on the negatively charged surface, which, in net shape electroforming applications such as tooling, is a model which is the inverse of the desired final shape. As a near net-shape forming technology, electroforming has certain drawbacks including extremely low deposition rate, the need to machine or otherwise produce an accurate mandrel or form, and the generation of toxic liquid and sludge by products.
Novel processes for additive manufacturing of net shape objects composed of metals are clearly needed. The technologies noted above are limited in their capability, use expensive equipment, and typically have safety hazards associated with the presence and handling of lasers, liquid metals and powders.
This invention is directed to a system and a method of fabricating an object by consolidating material increments in accordance with a description of the object using a process that produces an atomically clean faying surface between the increments without melting the material in bulk. In alternative embodiments, ultrasonic, electrical resistance, and frictional methodologies are used for object consolidation.
The material increments are placed in position to shape the object by a material feeding unit. The raw material may be provided in various forms, including flat sheets, segments of tape, strands of filament or single dots cut from a wire roll. The material may be metallic or plastic, and its composition may vary discontinuously or gradually from one layer to the next, creating a region of functionally gradient material. Plastic or metal matrix composite material feedstocks incorporating reinforcement materials of various compositions and geometries may also be used.
If excess material is applied due to the feedstock geometry employed, such material may be removed after each layer is bonded, or at the end of the process; that is after sufficient material has been consolidated to realize the final object. A variety of tools may be used for material removal, depending on composition and the target application, including knives, drilling or milling machines, laser cutting beams, or ultrasonic cutting tools.
The material increments are fed sequentially and additively according to a computer-model description of the object, which is generated by a computer-aided design (CAD) system, preferably on a layer-by-layer basis. The CAD system, which holds the description of the object, interfaces with a numerical controller, which in turn controls one or more actuators. The actuators impart motion in multiple directions. Three orthogonal directions may be used or five axes, including pitch and yaw as well as XYZ, may be appropriate for certain applications, so that each increment (i.e., layer) of material is accurately placed in position and clamped under pressure.
The system and method may incorporate the use of support materials to provide suitable substrates for any features of the object, which, when viewed sectionally, are overhanging. A description of the support resides in the CAD system, enabling the support to be built sequentially and additively. The support is preferably composed of less valuable material which is removed by stripping, cutting, dissolution, or by melting, when material having a lower melting-point than that of the object is used.
As examples, useful support materials include ceramics, particularly rapidly curing, water-soluble ceramics, and metal foils which do not bond but can be compressed so as to hold up the build portion. The support materials may be consolidated using the same power supply and different joining parameters, though not every layer or increment of the support need be bonded to the next layer, nor does the support need be fully consolidated. Indeed, weakly or partially bonded support material may be removed by breaking it up and shaking it loose using ultrasonic vibrations of appropriate frequency.
Other embodiments of the invention are directed to fabricating fiber-reinforced composites, including composites with continuous ceramic fibers in a metal matrix. According to one aspect, a layer of fibers is covered with a layer of a metallic powder, the surface of which is then partially consolidated by sweeping the surface with a laser beam. Full consolidation is effected using ultrasonic, electrical resistance, or frictional bonding techniques.
Another aspect is directed to fabricating an object by tape lay-up. Tape from a spool is fed and cut into segments to create successive sections of the object, the direction of the tape segments preferably alternating between two orthogonal directions from section to section. Material may also be provided in the form of wire or strip fed from a spool. Such a configuration is particularly applicable to repairing and overhauling worn or damaged regions of an object